The present invention is directed to the field of electrical motor vehicles with zero turning radius. It also relates to those vehicular designs in which steering of the vehicle is not done by moving the axles of the wheels.
There had been designs in the past, which utilized an electric motor inside the wheel. On many occasions the wheel is turned into a wheel motor (U.S. Pat. No. 5,894,902). But as there are no gears in the case of a direct-driven wheel motor, in order to generate a high torque, either the diameter or the thickness of the wheel motor has to be increased: This makes the wheel motor heavy. To hold together wheels with wheel motors, the axles and the chassis (or the shell) both have to be stronger and heavier than in a vehicle driven by a centrally located power pack.
How to do away with the numerous mechanical parts, which weigh down an electric motor vehicle? Moreover, how to reduce the rolling friction to reduce the cruising power requirement of an electric motor vehicle? These were the two major pointers leading to this invention. U.S. Pat. Nos. 4,163,567 and 4,192,395 disclose vehicles, which opened a way to finding suitable answers. The rigid coaxial nature of the two parallel wheels in those vehicles restricts the use of the vehicles to low traveling speeds. Further, the electrical drive motors for the two wheels are located outside the wheel hubs, which limits the number of motors used to drive each wheel without sacrificing useful windscreen width of the vehicles. The bearings of the annular wheels have no provisions to protect against foreign materials from getting into their engaging surfaces. The use of very large wheels does not eliminate other driving mechanisms outside the wheels, excepting a separate steering mechanism. The rigidity of the mounting of annular wheels on vehicle frame does not take into account, momentary radial impacts on the wheels while rotating as the vehicle travels. These impacts bring about point distortions in the wheel, increasing the friction in the rotation of the wheels.
On factory shop floors, there is a need for simple, low-maintenance traction vehicles of high maneuverability. A two-wheel design improves the negotiability of such a traction vehicle, if necessary features are built into existing art. The most important sought-after feature is to eliminate the need to reverse the vehicle to effect traction. Universal platforms or holonomic wheels are capable of smooth front-rear interchangeability; but they all have more complex tire structures, and have to be necessarily of more than two wheels (U.S. Pat. No. 4,715,460).
The construction of a two-parallel-wheeled vehicle is restricted by the maximum diameter a practical annular wheel can reach without sacrificing structural strength. For to have more carrying ability or to have more space in a vehicle with no conventional steering or driving mechanism, holonomic wheels are promising. U.S. Pat. Nos. 4,335,899, 4,598,782, 4,715,460, 5,246,238, 5,312,165 and 6,547,340 disclose evolving designs in holonomic wheel design. Except in U.S. Pat. No. 6,547,340, rest of the designs fail to compensate for the uneven wear in the rollers in case of rectilinear motion by the vehicle having such wheels. However, in U.S. Pat. No. 6,547,340, there is no control over the necessary rotation of each roller after it leaves ground contact as the holonomic wheel rotates and the vehicle travels. Further, the scheme of positioning of rollers in a four-wheeled vehicle (U.S. Pat. No. 4,598,782) always generates forces which are not in the direction of actual travel of the vehicle. These forces are also cancelled by the unique positioning. However, not before they have exerted bending stresses on each of the axles of the holonomic wheels. In addition, the workings of the design also depend upon the uniformity of the ground friction each of the wheels experiences. Nonuniform ground friction has to be compensated for by varying wheel rotation in response, as there is no direct control over the rollers on the holonomic wheels of existing art.